Maintenance of independence in old age depends, in part, on lower extremity function. Lean mass and strength both contribute to lower extremity function. Although the term sarcopenia suggests that muscle mass is the key factor, interventions on strength alone, rather than on mass alone, have been more effective in reversing disability. This project is multifaceted and is conducted through collaboration with several extramural investigators. It includes work with the Sarcopenia Initiative with the NIH Foundation, analysis of factors that might accelerate or prevent loss of lean mass, and projects focused on hypertrophy of muscle and change in fatty infiltration with interventions.